1. Field of the Invention
The present invention relates to a method and apparatus of detecting from the ground surface the location of an electrically insulative continuous or long length item located underground by the employment of electromagnetic waves.
Commonly, electrically conductive wires are generally required for underground pipe lines made of synthetic resin intended to transport, for example, city gas or city water.
2. Description of the Prior Art
In one prior art arrangement, a metallic wire is laid on the peripheral surface of an underground pipe made of synthetic resin, whereby the bare wire is subject to unavoidable corrosion.
Meanwhile, in another prior art arrangement, the electrically conductive wire is coated with an electrically insulative synthetic resin material for the prevention of corrosion of the underground wire. In the conventional arrangement as described above, however, if the electrically conductive wire should accidentally be broken or cut off by digging or excavation work in the ground, propagation of the electric current is completely interrupted, with consequent suspension of electromagnetic wave generation, thus making it utterly impossible to detect the location from the ground surface.
If the frequency of the electromagnetic wave is made extremely high, it may become possible to transmit the current from one cut end of the conductive wire to the other cut end thereof through the ground. However, in the case where the electromagnetic waves of such extremely high frequencies are to be employed, there is presented another problem that it becomes difficult to detect the conductive wire over a long distance from the point of power supply.
Moreover, for connecting the electrically conductive wires to each other, it is necessary to first remove the outer coating layers thereof for electrically connecting the core wires, while it is required further to cover the connected portions with putty or the like for protection against corrosion, and thus, a considerable amount of manual labor is required for such connecting operation.
Meanwhile, in situations where steel pipes are connected to the synthetic resin pipes, it has been a general practice to connect the bare wire or the wire covered with the outer coating layer, which is provided along the synthetic resin pipe, to the steel pipe by soldering or welding, and therefore, the connecting operation is further complicated undesirably.
Accordingly, it is an essential object of the invention to provide an improved method and apparatus of detecting an underground continuous length item by solving the technical problems as described above.
It is another important object of the invention to provide an electrically conductive wire for detecting an underground continuous length item of the above described type, which is electrically conductive, and which is free from undesirable corrosion.